The present invention relates generally to mixer circuits and particularly to such circuitry utilizing filter circuits.
Modern high frequency communication systems such as transceivers or equipment for testing such systems often include frequency converter or mixer circuits which can perform a variety of functions. For instance, it is desired that mixing circuitry be utilized in transceivers for providing an intermediate frequency (IF) signal at a first terminal in response to a local oscillator signal applied to a second terminal and a radio frequency (RF) input signal applied at a third terminal, when such equipment is operated in a "receive mode". It is also desired that the same circuitry be usable for converting the frequencies of a modulated signal applied to the first terminal to provide a desired output signal at the third terminal, when such equipment is operated in a "transmit mode" or as a signal generator.
Generally, prior art circuitry for performing mixing functions at frequencies of between 1 and 3 gigahertz (GH.sub.z) utilize complex, broadband transformers for cancelling unwanted signals. These transformers are expensive and tend to take up space and add excessive additional weight. Furthermore, some prior art systems require redundant circuitry to perform the functions of the above described "receive" and "transmit" modes.